Caption: Nasal polyp, light micrograph. Polyps are tumours (growths) that occur on mucus membranes. Nasal polyps are removed if they turn cancerous or begin to obstruct the air flow. This polyp developed as a result of chronic inflammation in the nasal cavity, such as in allergic rhinitis (pollen or dust allergy). The purple patches are white blood cells (plasma cells and eosinophils), important components of the body's immune system.